Generally, a scroll structure used for a rotary machine such as a turbine is disposed in front of a first stator blade (inflow side of working fluid) or behind a last rotor blade (outflow side of working fluid) in a turbine using heated steam or heated gas as the working fluid, and the scroll structure is a sheet metal welded structure through which the working fluid flows (see Patent document 1 for example).
A conventional scroll structure includes an upper casing and a lower casing which are divided by a horizontal surface, and the upper casing and the lower casing are fastened to each other using a bolt (see Patent document 2 for example).
The scroll structure has a heat shield effect with respect to a peripheral stationary member, and a rectifying effect for working fluid.
When working fluid which flows into or out of a turbine is high temperature, the scroll structure shields radiant and heat transfer from the working fluid, and prevents rise in temperature of a member in the peripheral stationary member such as an inner casing.
In this case, a material having high strength at a high temperature is selected as a material for the scroll structure. Further, in order to satisfy the material strength required to the scroll structure, an outer peripheral surface of the scroll structure is sprayed with cooling fluid to decrease the temperature of the scroll structure.
A channel in front of a first stator blade or behind a last rotor blade in the scroll structure is formed into such a shape that aerodynamics are taken into consideration so as to rectify working fluid. In this configuration, a pressure loss of the working fluid is suppressed, and the performance of the turbine is improved.    Patent document 1 Japanese Unexamined Patent Application, Publication No. H1-117929    Patent document 2 Japanese Examined Patent Application, Publication No. S60-6077